Laying pipe underground uses the three basic steps that are involved in burying anything in the ground—1) dig the hole; 2) put the thing to be buried in the hole; and 3) file the hole back up again. But, the process of putting long expanses of pipe underground creates unique problems. These projects can involve trenches that are up to several feet deep and wide, and extend for literally hundreds or even thousands of miles over all types of terrain and through all types of soils, from soft loam to hard pan; from level ground to 45-degree grades; and in all sorts of climatic conditions, from hot, dry and dusty to freezing and wet.
The pipe can be up to 4 or 5 feet in diameter (and sometimes larger) and may be made of concrete or plastic or other material, and may carry water, or oil, or natural gas, or sewage, or electrical wires, or fiber optic cables, for just a few examples.
The pipe-laying process involves first using a large trenching device that creates the trench. These machines typically deposit the excavated material, called “spoil,” along side the trench creating what is called the “spoil bank” or “spoil pile.” The spoil bank can be five to six feet high at its center line, and eight to ten or more feet wide at its base. It will include both small grain dirt or sand, but also larger rocks and aggregates. Its exterior crust might even be frozen. It might include debris such as broken parts from a trencher, or wire, bottles and cans, or wooden or metal posts, or just about anything that might be found in or on the ground.
The next step in the overall pipe-laying process involves placing the pipe into the trench. Because a rupture of one of these pipes could have disastrous safety and environment consequences, it is extremely important that the pipe be as well protected as possible. This typically means that the pipe will not be laid directly on the ground in the trench, but on sand bags or other such cushioning and positioning devices. It also means that the pipe will often be covered or coated with a protective material to prevent corrosion.
The next step in the overall process is backfilling the trench. When the trench is back filled, it is desirable to first completely encase the pipe with a relatively fine, flowable, defined and uniformly-sized backfill material so that the pipe is equally and evenly supported. This material is referred to as “fines” in the industry. Partially backfilling the trench with fines is called “padding” the pipe. Sometimes, a plastic sheeting strip will be placed in the trench on top of the padding as a warning to anyone who might subsequently be digging in the area (they would encounter the warning strip first thus alerting them to the presence of the pipe below before doing damage to the pipe).
The last step—completely filling up the trench—presents environmental concerns as there is a desire, particularly on these long, cross-country pipe laying projects that often traverse undeveloped land, to leave the area as clean, neat and environmentally sound as possible.
Therefore, it has long been known that simply bulldozing the spoil back into the trench was not acceptable. Because the spoil will often include rocks or other aggregate material of one size or another, simply bulldozing the spoil bank back into the trench may damage the pipe or its protective cover or coating as the rocks fall directly on it. Also, the rocks or aggregate material may create an unwanted and dangerous pressure point on the pipe. Or they may “bridge” in the trench, preventing the backfill material from flowing under and around the pipe, thus creating an unevenly supported pipe that might be more susceptible to leaking or, worst, rupture. Lastly, just bulldozing the spoil back into the trench can leave an unsightly job site.
In the earliest days of long-expanse pipe laying, suitable backfill material, such as sand, was trucked to the site and used as the padding material. This proved inadequate for reasons of cost primarily. As in almost all, if not all, competitive commercial activities, cost is an incredibly important factor in this industry. These large, pipe-laying projects can cost millions, if not ten's or hundred's of millions of dollars. Ways to improve the padding process and to do so at less cost are constantly being explored, and it is not surprising that trucking in the fine padding material was not acceptable for very long. Therefore, the industry began to process the excavated material on-site to separate the fines that could be used to pad the pipe from the coarser material.
Some of the earliest machines to separate the fines from the coarser material were portable screening apparatuses (see, e.g., U.S. Pat. No. 3,439,806) that could be moved to the trench site. This required, however, that other equipment be used to bring the spoil to the screening apparatus, and to transport the fines back to the trench.
It was soon determined, however, that an integrated machine that could perform all of these steps; that is, picking up the spoil, delivering it to the screening apparatus, and then transporting the fines to the trench, leaving the coarser material behind, would be a marked improvement. One of the earliest such integrated machines is shown in U.S. Pat. No. 3,701,422, issued on Oct. 31, 1972 to Thomas A. Downey. It discloses what is essentially a converted large scale scraper. These large wheeled scrapers typically have a cutting blade that is intermediate of the front and back wheels on a long wheel-based vehicle, and is hydraulically raised or lowered by the driver to remove a layer of ground while the vehicle moves forward. The excavated dirt is stored in the large holding vessel immediately behind the cutting blade. When the holding vessel is full, the scraper travels to a predetermined area where it is unloaded, and the scraping process begins again. In the '422 patent, Downey converted the scraper into a padding machine by adding an “up” conveyor immediately behind the cutting blade in the space formerly devoted to the holding vessel in the scraper. The vehicle straddled the spoil pile next to the trench, and the cutting blade caused the spoil to be forced onto the up conveyor where it was carried to and dumped onto a screen. The fines fell through the screen onto a cross-pass conveyor which carried the fines back to the trench. The coarser material that would not fall through the screen fell onto a another cross-pass conveyor that deposited the coarse material back onto the ground on the side of the device opposite the trench. This device thus incorporated the three basic components of all integrated padding machines that have followed since—1) the up conveyor for elevating and transporting the spoil to (2) a screening assembly which allows the fines from the spoil to fall through the screen onto a (3) cross-pass conveyor that transports the fines back to the trench.
Since then, there has been a continuing effort to improve the padding machine and process. In terms of padding pipe, “improvement” can mean many things. For example, cost continues to be primary factor. This means speed, among other things. For example, large scale pipe-laying projects preferably want to lay at least one linear mile of pipe per day. That dictates that all of the processes—digging the trench, laying the pipe, and, as is important here, padding the pipe, must occur at that rate. The normal work day on a pipe-laying project is 10 hours. That means that the preferred padding machine must be able to pad at least 8.8 feet of pipe every minute. When the unavoidable down time for fueling, lubricating, cleaning screens, etc., is factored in, the preferred padding machine must be able to pad pipe at something greater than 8.8 feet per minute. That in turns means that the padding machine should be able to handle different terrains, different spoil bank contents, and different environment and weather conditions effectively and efficiently. It also means that the preferred padding machine must be able to extract from the spoil bank the maximum amount of fines possible. Padding specifications usually dictate that the padding material must extend above the highest point of the pipe by a minimum amount, usually six or more inches. It is therefore necessary that the padding machine be able to generate sufficient fines from the spoil bank to be able in turn to deliver the appropriate amount of fines back to the trench in a single pass at a sufficiently high rate of forward movement of the padding machine. As can be appreciated, if the padding machine must stop, reverse direction, and then re-pad an area, average forward speed is adversely affected.
In a nutshell, the padding operation prefers a padding machine that can consistently and uniformly deliver a high quality of fines, a high quantity of fines, and at a high rate of average forward speed.
As mentioned, the desire to improve the modern padding machine has continued literally unabated. Just since 1985, more than thirty U.S. patents have issued relating in one fashion or another to padding machines and the method for their use. For example, in U.S. Pat. No. 4,633,602, issued to Ricky Layh et al on Jan. 6, 1987, an integrated padding machine is disclosed that has the traditional up conveyor, screening assembly and cross-pass conveyor, but which claimed a novel adjustable “gathering head” at the leading end of the up conveyor that could be adjusted by the operator to gather more or less of the spoil bank.
In U.S. Pat. No. 4,912,852, issued to William B. Bishop et al on Apr. 3, 1990, a “Backfill Machine” is disclosed that includes the traditional up conveyor, screening assembly and cross-pass conveyor, and also includes a hydraulically powered front auger that assists in moving spoil onto the up conveyor. The auger, however, has no effective digging or crushing capability. The claimed novel aspect of the device disclosed in '852 is that the cross-pass conveyor is situated so as to redeposit the fines back into the trench at a point in front of the front auger.
In U.S. Pat. No. 4,948,299, issued to Thomas J. Cronk, Jr. et al on Aug. 14, 1990, a padding machine is disclosed which again includes the traditional up conveyor, screening assembly and cross-pass conveyor, in which the claimed novel aspects are multiple conveyors and screens to extract more fines from the processed spoil.
In U.S. Pat. No. 5,120,433, issued to Mark Osadchuk on Jun. 9, 1992, an improved padding machine, again having the traditional up conveyor, screening apparatus and cross-pass conveyor, is disclosed in which a pair of forwardly extending guide projections, each having a flat, planar, lower ground engaging surface, guide the spoil into and onto the up conveyor. (See also, related U.S. Pat. Nos. 5,195,260, 5,363,574, and 5,430,962, which all disclose a similar padding machine having the forward extending guide projections, some with rotary feeding wheels attached to the guide projections and other similar means for guiding the spoil into and onto the up conveyor, and having means for applying a downward pressure on the front guide means).
In U.S. Pat. No. 5,421,108, issued to Teddy L. Stewart on Jun. 6, 1995, a “High Volume Pipe Padding Machine” is disclosed that has the traditional up conveyor, screening assembly and cross-pass conveyor, and is designed to be attachable to the back of a standard bulldozer. The machine has a front cutting blade that can be raised or lowered by the operator to increase or decrease the amount of spoil being fed to the up conveyor. (See also, related U.S. Pat. No. 6,125,558).
And perhaps most recently, U.S. Pat. No. 6,318,930 B1, issued to Erik D. Scudder on Nov. 20, 2001, discloses a padding method and apparatus that has an adjustable “feeder housing” that extends forwardly of the up conveyor and a hydraulically-operated rotating drum that assists in breaking up dirt clods.
As this sampling of patents ably shows, the desire to improve upon the traditional padding machine continues, as there is an ongoing need in the art for a padding machine that produces a higher quality and quantity of fines, and does so efficiently, effectively and expeditiously, regardless of the terrain, soil, debris or climatic conditions encountered, and that presents minimal adverse impact to the terrain.
While these existing machines are all functional to a degree, none of them provides the advantages obtained by the machine herein disclosed and described. None of the prior art machines provides both effective digging and crushing capability by incorporating a true digging auger (i.e., one that is preferably mechanically driven rather than being hydraulically driven) previously used in road planers and the like, that not only acts to deliver the spoil to the up-conveyor as in prior art machines, but also digs and crushes to produce a higher percentage of fines. Many of the prior art devices have one means or another for introducing the spoil to the up-conveyor, but they do not do so in the same way and with the same result as does the machine of this invention. For example, in the device shown in the '433 patent (and its related patents noted above), the forwardly extending guides that are used to guide the spoil onto the up conveyor actually have a tendency to create dirt clods if there is any moisture in the spoil. Those dirt clods are simply passed through the machine, thus diminishing the production of fines instead of enhancing it. Not only does the machine of this present invention not create dirt clods, but with the combination of the digging auger and breaker bar, it breaks apart the dirt clods and grinds aggregate material that are already present in the spoil pile.
None of the prior art machines can effectively pad pipe at a 45 degree up-grade; none of the prior art machines constantly monitors the amount of padding so that the operator can ensure that enough but not too much padding is being added to the trench; none of the prior art machines provides truly enhanced operational control; none of the prior art machines can be effectively used in freezing conditions; none of the prior art machines provide screens that can be effectively used with wet and grassy spoil; and none of the prior art machines provides means for effective dust control or for padding in freezing conditions. There exists a need in the art for an improved padding machine that can do all of these things and more, which is what is provided by the invention hereinafter described and claimed.